Riding mowers having a zero radius turn (ZRT) capability are well known in the mowing art. Such mowers have a frame that carries a power source, such as an internal combustion engine, for propelling the frame over the ground and for providing power for mowing. Two powered rear drive wheels are carried on the frame with the front of the frame having a pair of unpowered front wheels, the wheels collectively supporting the frame for rolling over the ground. Often, the unpowered front wheels are caster wheels.
The rear drive wheels in a ZRT mower are individually powered by separate hydraulic drive motors that receive pressurized hydraulic fluid from a hydraulic system driven by the power source of the mower. The drive motors are individually controlled by separate control levers placed adjacent an operator's seat provided on the mower frame. The mower is steered by advancing one lever farther than the other to cause one drive motor, and thus the drive wheel on one side of the mower, to rotate faster than the other drive motor and drive wheel, thereby causing the vehicle to turn. Very sharp spin or ZRT type turns can be accomplished by advancing one control lever forwardly while pulling the other control lever rearwardly to cause the drive wheels on the opposite sides of the mower to simultaneously rotate in opposite directions.
A rotary cutting deck is carried at the front of the mower. The cutting deck usually houses a plurality of cutting blades that rotate about substantially vertical axes to cut grass in horizontal cutting planes. The blades are typically staggered relative to one another with a center blade being offset forwardly of a pair of side blades located on either side of the center blade. This allows the orbits of the cutting blades to overlap without having the blades contact one another, thus avoiding the need for timing the rotation of the blades. As the mower is driven over the ground and the blades are rotated, the blades cut a relatively large unbroken swath of grass during each pass of the mower. Exmark Mfg. Co., Inc. manufactures and sells ZRT mowers of this type under its Lazer Z brand name.
To change the height of cut of the grass, the cutting deck is vertically moved up and down relative to the mower frame and thus relative to the ground to change the height of the cutting blades relative to the ground. In many known mowers, the HOC system used to do this includes multiple suspension links to the cutting deck. These movable links move up and down simultaneously with one another under the action of a single control lever. The control lever has a plurality of discrete adjusted positions relative to the mower frame, often established by the control lever engaging against a pin, to allow the height of cut of the cutting deck to be adjusted in a plurality of discrete increments. The height of cut is adjusted by changing the location of the pin within an array of adjustment holes provided therefor on the mower frame. The pin is selectively inserted by the operator into whichever adjustment hole corresponds to the desired height of cut.
In HOC systems of this type, it is desirable to be able to level the cutting deck relative to a reference plane, such as a ground plane or a rake angle plane. This can be done in prior art mowers by adjusting the effective distance between the suspension links and the cutting deck. However, in making the cutting deck leveling adjustments, the actual height of cut might vary from the nominal height of cut provided by the location of the pin at the completion of the cutting deck leveling adjustments. Thus, the operator will have to readjust the cutting deck leveling adjustments until the cutting deck is level to the desired plane at the same time the actual height of cut corresponds to the nominal height of cut. This can be a cumbersome, time consuming and labor intensive adjustment operation.
Further, the pin/hole type of HOC system provides only a plurality of discrete heights of cut. Infinite heights of cut can be obtained using threaded adjusters, but such adjusters require many turns to adjust the height of cut over a wide range of travel. Thus, it would be desirable in HOC systems to provide a system in which discrete heights of cut can be easily and quickly selected, such as by inserting a pin within a selected hole, but which would also permit the operator to quickly and easily obtain heights of cut in between the preset discrete heights of cut.
The cutting decks used on mowers of this type are often quite large and heavy. Counterbalance springs have been used in prior HOC systems to help the operator lift the cutting deck when going from a lower to a higher height of cut. However, most HOC systems of this type use a pair of tension springs as counterbalance springs. These springs surround a pair of longitudinal connecting rods that run over the top of the cutting deck adjacent opposite sides of the mower. Such springs are typically exposed and in plain view due to the location of the connecting rods. Thus, to some extent, the springs are prone to being damaged and present an obstacle that the operator has to step over if the operator were to attempt to mount the mower from either side of the cutting deck.